🦎 Evolution

Evolution

Change in the inherited characteristics of populations over successive generations.

Natural Selection

Individuals with traits better suited to their environment survive and reproduce more, passing those traits on.

Charles Darwin

The naturalist who proposed natural selection in On the Origin of Species in 1859 after the Beagle voyage.

Adaptation

A heritable trait that improves an organism's survival and reproduction in its environment.

Fossils

Preserved remains or traces of ancient organisms that record the history of life.

Common Ancestry

All living things descend from shared ancestors, evidenced by universal DNA and genetic code.

Homologous Structures

Body parts with similar structure from a common ancestor but different functions, like a human arm and bat wing.

Analogous Structures

Similar-looking features with different origins that evolved independently for similar function, like bird and insect wings.

Vestigial Structures

Reduced features retained from ancestors that have lost most of their original function, such as the human appendix.

Variation and Selection Pressure

Environmental factors like predators or climate that favour certain heritable variants over others.

Antibiotic Resistance Evolution

Bacteria with resistance genes survive antibiotic use and multiply, making resistance more common.

Peppered Moth

A classic example of directional selection in which dark moths became common in polluted industrial Britain.

Extinction

The permanent disappearance of a species, occurring naturally and at accelerated rates today.

Artificial Selection

Humans breed organisms with desired traits, creating crops and dog breeds from wild ancestors.

Intermediate topics (20)

Species Concept

The biological species concept defines a species as a group of interbreeding natural populations reproductively isolated from others.

Speciation

The formation of new species when populations diverge enough to become reproductively isolated.

Allopatric Speciation

Speciation after a geographic barrier separates populations, as with Darwin's finches on separate islands.

Sympatric Speciation

New species arising within the same area, often through polyploidy or ecological specialisation.

Reproductive Isolation

Prezygotic and postzygotic barriers that prevent gene exchange between species.

Directional Selection

Selection favouring one extreme phenotype, shifting the population mean in one direction.

Stabilising Selection

Selection favouring intermediate phenotypes, as seen in human birth weight.

Disruptive Selection

Selection favouring both extremes over the average, which may lead to divergence.

Sexual Selection

Selection arising from competition for mates or mate choice, creating traits like peacock tails.

Fitness

An organism's relative contribution of offspring to the next generation.

Adaptive Radiation

Rapid diversification of a lineage into many forms filling different niches, as with Hawaiian honeycreepers.

Convergent Evolution

Unrelated lineages evolve similar traits because they face similar selective pressures.

Divergent Evolution

Related species become increasingly different as they adapt to separate environments.

Coevolution

Reciprocal evolutionary change in interacting species, such as flowers and their pollinators.

Phylogenetic Trees

Branching diagrams that show inferred evolutionary relationships among species.

Cladistics

A classification method grouping organisms by shared derived characteristics into clades.

Molecular Clock

Uses the steady rate of neutral mutations to estimate when lineages diverged.

Mass Extinctions

Five major events, including the end-Permian and end-Cretaceous, that wiped out large fractions of species.

Origin of Life

Hypotheses such as the primordial soup and RNA world explain how self-replicating molecules first arose.

Human Evolution

The hominin lineage, from Australopithecus through Homo erectus to Homo sapiens, evolved in Africa.

Advanced topics (19)

Neutral Theory

Proposes that most molecular variation results from drift of selectively neutral mutations rather than selection.

Kin Selection

Natural selection favouring behaviours that help relatives, explained by Hamilton's rule rb greater than c.

Evolutionary Developmental Biology

Studies how changes in developmental genes, such as Hox genes, produce evolutionary novelty.

Punctuated Equilibrium

Suggests species remain stable for long periods interrupted by short bursts of rapid change.

Founder Effect and Bottleneck

Loss of genetic diversity after a few individuals found a new population or numbers crash.

Red Queen Hypothesis

Species must constantly evolve just to keep pace with coevolving enemies such as parasites.

Horizontal Gene Transfer

Movement of genes between unrelated organisms, important in bacterial evolution.

Gene Duplication

Extra gene copies free one copy to acquire new functions, fuelling evolutionary innovation.

Evolutionary Stable Strategy

A strategy that, once common in a population, cannot be invaded by any rare alternative.

Maximum Likelihood Phylogenetics

Statistical methods that choose the tree and substitution model most likely to have produced observed sequence data.

Cambrian Explosion

A rapid diversification of animal body plans about 540 million years ago.

Ancient DNA

Sequencing of DNA from fossils and remains to reconstruct population history, such as Neanderthal admixture.

Evolutionary Trade-offs

Improving one trait often costs another, constraining which adaptations can evolve.

Experimental Evolution

Long-term laboratory studies, like Lenski's E. coli, that watch evolution happen in real time.

Macroevolution

Evolutionary patterns above the species level, including origins of major groups and mass extinctions.

Selective Sweeps

A beneficial allele rising to fixation reduces nearby genetic variation through hitchhiking.

Evolution of Sex

Hypotheses explain why sexual reproduction persists despite its costs, including the Red Queen and mutation clearance.

Phylogeography

Studies how historical processes shaped the geographic distribution of genealogical lineages.

Speciation Genomics

Genome-wide analysis that identifies the loci and islands of divergence responsible for reproductive isolation.